In the field of lubrication, cutting fluids are typically made from mineral oils and contain emulsifying materials which enable stable aqueous emulsions to be produced. In practice, cutting fluid emulsions are subjected to biodegradation as they are ideal breeding grounds for bacteria. The presence of bacteria is very troublesome as it can lead to breakdown of cutting fluid emulsions, corrosion of machined parts and shortened tool life as well as being a potential health hazard. It is therefore important that cutting fluid emulsions should contain corrosion inhibitors and biocides to inhibit or prevent bacterial growth. This may be achieved by regular addition of biocides to cutting fluid emulsion, but it is preferable that cutting fluids, as supplied by the manufacturers, contain biocidal materials.
Boron compounds, particularly alkali metal borates, are known to be both corrosion inhibitors and effective biocides. Various proposals have been made to incorporate boron compounds into lubricants as they are known to have important lubricating properties as well as being corrosion inhibitors and biocides. However, the use of alkali metal borates for these applications, although attractive, is accompanied by the inherent difficulty of preparing a suitable dispersion of an inorganic salt in a mineral oil. Therefore, an effective and economical way of solubilizing an alkali metal borate in a mineral oil is desirable.
U.S. Pat. No. 3,853,772 describes a lubricating oil containing a dispersion of alkali metal borate. British Pat. No. 1,306,211 describes the preparation of oil additives by reaction of boric acid with a surfactant in the presence of a metal alcoholate.